1. Field of the Invention
The present invention relates to a toggle lever clamping apparatus for an injection molding machine and, more particularly, to a toggle lever clamping apparatus for an injection molding machine, having a movable platen support member disposed movably on a base frame for supporting the movable platen movably along tie bars, and capable or linearly moving the movable platen relative to a stationary platen to open and close a mold an of producing a clamping force to clamp the mold.
2. Description of the Related Art
A conventional toggle lever clamping apparatus for an injection molding machine is provided with a movable platen support member which is capable of moving on a base frame. This movable platen support member is attached to a lower part of a movable platen to support it so that the toggle type clamping system achieves stable mold opening and closing operations maintaining the parallelism of the movable and the stationary mold. The movable platen support member has a frame, and rollers or wedge-shaped sliders (linear guides in some cases) supported on front and back parts of the frame on the front and the back side of the movable platen, respectively. The movable platen support platen member prevents the tilting of the movable platen during the movement of the movable platen for mold opening and closing operations, suppresses the bending of the tie bars when the movable part of the mold is attached to the movable platen and maintains the parallelism of the movable and the stationary part of the mold when the mold is opened and closed.
Referring to FIG. 4, a conventional toggle lever clamping system for an injection molding machine includes a stationary platen 32 fixedly set on a base frame 31 to support a stationary part 43 of a mold, a link housing 33 placed near the left end, as viewed in FIG. 4, of the base frame 31 so as to be movable toward and away from the stationary platen 32, tie bars 32 extended through the four corners of the stationary platen 32 and the link housing 33, a movable platen 36 disposed opposite to the stationary platen 32, engaging the tie bars 34 and capable of holding the movable part 42 of the mold, a toggle link mechanism 37 having opposite ends respectively attached to the link housing 33 and the movable platen 36, a movable platen support member 44 provided with a front roller 45 and a back roller 45 capable of rolling on the base frame 31.
When closing and clamping the mold, the conventional toggle lever clamping system exerts forces F1 and F2 on the movable platen 36. The forces F1 and F2 strain the movable platen 36 such that the back surface of the movable platen 36 is stretched and the movable platen 36 warps in the direction of the forces F1 and F2 accordingly. As the movable platen support member 44 prevents the movable platen 36 from warping and force F2 presses the back roller 46 of the movable platen support member 44 strongly against the base frame 31, which affects the life of the movable platen support mechanism 44 significantly and, in some cases, causes the movable platen support member 44 to be broken.
A force F4 caused by a reaction force F3 that acts on the lower back part of the movable platen 36 prevented from being warped by the force F2 acts on an upper part of the movable platen 36. Thus, the upper and the lower part of the movable platen 36 are warped differently. The unbalance in warping between the upper and the lower part of the movable platen 36 causes uneven application of mold clamping force to the mold causes irregular thickness distribution in the walls of a molding or difference in the amount of a molding material injected into the cavities of the mold between the cavities when the mold is a multicavity mold.
Accordingly, it is an object of the present invention to provide a toggle lever clamping apparatus for an injection molding machine, capable or solving the aforesaid problems in the conventional toggle lever clamping apparatus, of carrying out stable mold opening and closing operations, and of applying a mold clamping force uniformly to the mold to enable molding highly accurate moldings which are not different from each other in size and weight.
According to a first aspect of the present invention, a toggle lever clamping apparatus for an injection molding machine, comprises: a movable platen support member disposed movably on a base frame for supporting a movable platen supported on and guided for movement by tie bars; a toggle link mechanism for linearly moving the movable platen relative to a stationary platen to open and close a mold and for applying mold clamping force to the movable platen to clamp the closed mold; and a cushioning means for absorbing a component of the clamping force that acts on the movable platen support member when the mold is clamped so that the movable platen is allowed to be deformed for balance.
The toggle lever clamping apparatus is capable of achieving stable mold opening and closing operations, and the cushioning mechanisms included in the movable platen support mechanism permits the deformation of the movable platen when the mold is clamped. Consequently, the mold clamping force can be uniformly applied to the mold and accurate moldings which are not different from each other in size and weight can be obtained.
According to a second aspect of the present invention, the cushioning means includes a elastic member for supporting the lower back end of the movable platen on the base frame.
This toggle lever clamping apparatus is capable of achieving stable mold opening and closing operations, and the elastic mechanism included in the movable platen support mechanism permits the deformation of the movable platen when the mold is clamped. Consequently, the mold clamping force can be uniformly applied to the mold and accurate moldings which are not difficult from each other in size and weight can be obtained.
The elastic means may include coil springs or coned disk springs.